1. Field of the Invention
The present invention relates to a bump electrode structure and a method for forming the same, and more specifically to a bump electrode structure formed on a printed wiring board for solder-connection, and a method for forming the same.
2. Description of Related Art
A typical example of a conventional bump electrode formed on a printed wiring board for solder-connection, is so configured that, as shown in FIG. 1, in a glass-epoxy board 16 having a semiconductor device chip 15 which is die-bonded within a recess formed in one surface of the glass-epoxy board 16 and which is connected to patterned wiring conductors 13A through connection wires, the chip and the connection wires being encapsulated by a resin 14, electrode lands are formed on the other surface of the glass-epoxy board 16 in which the chip is not located, and a predetermined amount of solder is piled on each electrode land so as to form a solder bump 13 (See Japanese Patent Application Laid-Open Publication No. JP-A-61-174752 or English Abstract thereof, the disclosure of which are incorporated by reference in its entirety into this application). The solder forming the solder bumps 13 is supplied by, for example, a solder dip process, a solder paste printing process, or a method using a solder ball electrode, typified by a ball grid array (abbreviated "BGA").
In the case of mounting a package having solder ball electrodes, on a printed wiring board, in order to realize a reliable mounting and to obtain a desired degree of connection reliability, it has been considered to be required that an electrode size is on the order of 0.6 to 1.0 mm, and an electrode pitch is on the order of 1.27 to 1.5 mm.
On the other hand, as a conventional method for utilizing a connecting bump electrode formed by an electroplating, a TAB (Tape Automated Bonding) process has been known. Referring to FIG. 2, there is shown a sectional view illustrating this second conventional example.
In the second conventional example, as shown in FIG. 2, a film lead 21 formed on an insulating film 17 and having a bump electrode 18 formed at a tip end thereof is connected to a semiconductor device chip 15A located on a heating stage 20, with the intermediary of the bump electrode 18, by action of a pulse-heated tool 19. The bump electrode 18 is formed by piling, for example, copper, nickel, cold or the like. Since the connection is realized by a eutectic bonding by the pulse-heated tool 19, a satisfactory connection can be obtained if the height of the bump electrode is on the order of 20 .mu.m.
However, in packaging by using the conventional bump electrodes as mentioned above, the following disadvantages have been encountered:
In the case of the solder connecting, in order to avoid a defective connection such as a short-circuiting caused by a solder reflowing, and in order to ensure a reliability after the connection has been made, the electrode pitch is required to be at least on the order of 1.27 to 1.5 mm, as mentioned hereinbefore. This is a large restriction in reducing the size of the package and in increasing the number of external terminals.
In the conventional bump electrode formed by the electroplating, on the other hand, the structure is not so made to have a sufficient electrode height, and therefore, this bump electrode cannot be applied to a solder packaging. On the other hand, it inevitably needs a tool, such as the heating tool, which is not required in the solder packaging.